Adhesive



Patented Dec.-

UNITED STATES PATENT" OFFlCE arouse Paul B. Davidson, Wilkinsburg, Pa., and Julius R. Adams, Westfleld, Mass, assignors .to Old Colony Envelope Company, Westfleld, Mass, a corporation of husctts No Drawing. Application March 17, 1941-, Serial No: 383,793

4 Claims. (Cl. 106-213l This invention relates to improvements in adhesives and is more particularly related to socalled gums for use in connection with such devices as envelopes where it is desired-t adhesively secure together adjacently-disposed paper surfaces.

This application is a continuation in part of an application Ser. No. 202,882 filed by us on April 19, 1938, issued as Patent No. 2,241,709. It is a principal object of the invention to provide an adhesive for use with paper which is so constructed chemically that it will not discolor or otherwise deteriorate with age. That is,to say, we have conceived an adhesive which will not have the tendencyto discolor regardless of climate or other conditions under which the envelopes or other'articles are stored.

It has always heretofore been a. serious difiiculty in the envelope industry that the envelopes,

after storage on shelves or the like, become discolored due to chemical reaction between the gum or adhesive and elements in the paper. It appears that the cause of discoloration is the formation of colored or humus-like substances due to reaction between degraded protein which is necessarily present in any ordinarily sized paper and the reducing sugars present in any ordinary paper adhesive.

A further object of the invention is the pro vision of an envelope adhesive having special properties and characteristics particularly adapting them for use in the manufacture of envelopes. It-is the usual practice in the industry to apply the gum to the envelopes by machine and it will be appreciated that in order that application of the gum be carried on eiiiciently and economically, the gum must remain sufiiciently fluid and non-pasty for an ample length of time. The gums of this invention not only have the non-discoloration properties abovementioned but also they are properly fluid for use in the envelope-machine.

After considerable research we have come to the conclusion that discoloration can be eliminot capable of causing discoloration.

Our invention consists broadly in providing paper adhesives which have as a base a certain amount of partially-dextrinized starch and con- 55 Dr. H. C. Sherman.

position is properly fluid to permit eificient application to the paper by the machines and it is also such that it will not, after application to the paper, tend to react with more or less degraded protein in the paper sizings so as to form colored compounds which are objectionable.

After considerable experiment we have found that any gums or adhesives which contain appreciably more than 2% by weight of reducing sugars do react unfavorably with the protein in ordinary paper sizings so as to produce discoloration. In other words, we provide an adhesive composition which is so constructed chemically as to have a total reducing sugar content which is preferably not more than 2% by weight of the gum and we accomplish this by a combination of partially-dextrinized starch and a fluidifyin agent which is calculated to produce the desired efiect.

Careful and scientifically conducted experiments have clearly shown us that when the reducing sugar content of the gum does rise appreciably above the percentage mentioned, there is, inevitably, discoloration. Forexample, a number of pieces of paper, all the same kind, were stuclr together with various adhesives which have been heretofore known and with adhesives of this invention which are about to be described.

These pieces were aged under standardized conditions approximately natural ageing by being placed in test tubes, sealed, and placed in an oven regulated to C. for 48 hours. Discoloration appeared in the pieces which were not gummed with the adhesives of this invention so we proceeded to determine the reducing sugars'in all of the sample gums.

This was done by diluting a sample of each ducing sugar determination in accordance with the common and well-known method described as the Defrens method on page 74 of the second edition of Methods of Organic Analysis by low 2%, all other things having been kept equal.

We have further found that there are particular types of dextrin or starch which are most suitable for accomplishing our purpose. While, as a general rule, best results can be obtained if the reducing sugar content ofthe dextrin it self before cooking isbelow 2%, it is necessary that the final cooked gum contain less than 2% of reducing sugar to completely avoid discoloration.

That is to say, the hydrolysis that takes place during the normal cooking of the gum may objectionably increase the reducing sugar content even though the content of the original dextrin was low. Accordingly, we preferably use a partially-dextrinized starch which is of such a composition that when it is cooked for about thirty minutes at a temperature of around 98 C. with an approximately 40% concentrated solution of acetic acid, it will have, upon cooling, a reducing sugar content of less than, or at least not appreciably more than, 2% by weight.

Another example of a preferred dextrin is one which, when cooked for about thirty minutes at a temperature of about 85 C. with the same acetic acid, will not have a reducing sugar content of 'more than 2% by weight. That is to say, of all the variously dextrinized starches which are commercially available those which have the just-referred-to qualifications are most suitable for the practice of this invention.

When using the terms dextrin" or "partiallydextrinized stare hereafter, we mean just such substances as have been above defined. We found that while such cooked mixtures as have just been described might have the desired low reducing sugar content, they were not suiliciently fluid for application to the paper by the machines so that it was accordingly incumbent upon us to iiuidify the mixtures in a way whichwould not increase appreciably this reducing sugar content so as to later produce the objectionable discoloration.

As stated, the common way to fiuidify heretofore has been to add more, sugar but this, of course, increases the reducing sugar content so that the resulting adhesive would have have all of the objections which our invention overcomes.

Suchsubstances as we have found to produce the desired result include the esters of carbamic acid such as ethyl carbamate, methyl carbamate, and butyl carbamate. It seems to be immaterial whether condensation products are formed with the carbohydrate constituents during the manufacture of the gum, and it is a fact that the homologous mixture produced by the addition of our fluidifying substances to partiallydextrinized starch and water produces the desired result as long as the total reducing sugar content of the gum is less than 2% by weight.

According to the preferred form of the method of this invention, water and the partially dextrinized starch are mixed intimately. If desired, a volatile acid, such as acetic or the like, may. be introduced into the mixture to aid in the hydroly- 'Water Partially dextrinized starch; 501:0 62

sis of the starch and the mixture is then agitated so that the ingredients thoroughly blend with one,

another.

The composition is then heated in any wellknown manner to within a range of preferably from 160 to 212 E, which temperature is preferably maintained for from 20 to 60 minutes. The length of time during which the gum is cooked. depends, of course, on the size of the batch, the temperature, the equipment used and various other factors.

In any event, it is desirable that the mixture be cooked only until the hydrolysis of the starch to the desired degree of dextrinization is complete and not for such a length of time that the reducing sugar content be substantially increased.

We now add the fluidifying agentbut it is here desired to point out that we do not wish to be limited to any specific order in which the above ingredients may be added. It only is essential that the fluidifying agent be added to the composition at sometime.

As final steps in the process the gum is preferably chilled to about F., or below, after which the mixture is ready to be drawn.

While the proportions of the above ingredients may be greatly varied, very favorable results have been obtained when staying within the followin approximate ranges of proportions by weight:

Per cent 10 to 18 Fluidifying agent 3 to-10 1. As a new article of manufacture, an envelope adhesive having a reducing sugar content of not more thansubstantially 2% of the weight thereof, comprising in combination, partially-dextrinized starch, and an ester of carbamic acid group consisting of ethyl carbamate, methyl carbamate and butyl carbamate adapted to fluidify the adhesive for a suflicient length of time to permit its proper application to the envelopes by the envelope machines and to render the adhesive incapable of causing discoloration after being applied .to the envelopes. 1

2. As a new article of manufacture, an envelope adhesive having a'reducing sugar content of not more than substantially 2% of the weight thereof, comprising in combination, partially-dextrinized starch, and an ester of carbamic acid adapted to fluidify the adhesive for a sufficient length of time to permit its proper application to the envelopes by the envelope machines and to render the adhesive incapable of causing discoloration after being applied to the envelopes, said ester consisting of ethyl carbamate.

3. As a new article of manufacture, an envelope adhesive having a reducing sugar content of not more than substantially 2% of the weight thereof, comprising in combination, partially-dextrinized starch,,and an ester of carbamic acid adapted to fluidify the adhesive for a suflicient length of time to permit its proper application to the envelopes by the envelope machines and to render the adhesive incapable of causing discoloration after being applied to the envelopes, said ester consist ing of methyl carbamate.

4. As a new article of manufacture, an envelope adhesive having a reducing sugar content of not more than substantially 2% 01 the weight thereof, comprising in combination, partiallydextrinized starch, and an ester of carbamic acid adapted to fluidity the adhesive" for a sufiicient length of time to permit its proper application to 

